michael moll (cern/ph) 3 rd mc-pad network training event, jožef stefan institute, ljubljana,...
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Michael Moll (CERN/PH)
3rd MC-PAD Network Training Event, Jožef Stefan Institute, Ljubljana, Slovenia
- 29 September 2010 -
Radiation Hardness of Semiconductor Detectors- Radiation Effects and Detector Operation -
… including an introduction to ongoing radiation tolerant sensors developments
-1-Michael Moll – MC-PAD Network Training,
Ljubljana, 27.9.2010
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -2-
Outline
· Motivation to develop radiation harder detectors · LHC upgrade and expected radiation levels· Radiation induced degradation of detector performance
· Radiation Damage in Silicon Detectors· Microscopic damage (crystal damage), NIEL
· Macroscopic damage (changes in detector properties)
· Approaches to obtain radiation tolerant sensors· Material Engineering
• New silicon materials – FZ, MCZ, DOFZ, EPI• Other semiconductors: Diamond, SiC, GaN, ….
· Device Engineering• p-in-n, n-in-n and n-in-p sensors, 3D sensors and thin devices
· Silicon Sensors for the LHC upgrade ….. open questions and ongoing developments
· Summary
For details on LHC detectors
see lecture ofPhil Allport
For details on sensor production
see lecture ofManolo Lozano
For surface effectssee lecture of
G.-F. Dalla Betta
For details on radiation induced defects
see lecture ofIoana Pintilie
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -3-
LHC example: CMS inner tracker
5.4 m
2.4
m
Inner TrackerOuter Barrel
(TOB)Inner Barrel (TIB) End Cap
(TEC)Inner Disks(TID)
CMS – “Currently the Most Silicon”· Micro Strip:· ~ 214 m2 of silicon strip sensors, 11.4 million strips· Pixel:· Inner 3 layers: silicon pixels (~ 1m2) · 66 million pixels (100x150mm)· Precision: σ(rφ) ~ σ(z) ~ 15mm· Most challenging operating environments (LHC)
CMS
Pixel
93 cm
30 cm
Pixel Detector
Total weight 12500 t
Diameter 15m
Length 21.6m
Magnetic field 4 T
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -4-
B-layer (R=3.7 cm): 2.5×1016 neq/cm2 = 1140 Mrad2nd Inner Pixel Layer (R=7 cm): 7.8×1015 neq/cm2 = 420 Mrad1st Outer Pixel Layer (R=11 cm): 3.6×1015 neq/cm2 = 207 MradShort strips (R=38 cm): 6.8×1014 neq/cm2 = 30 MradLong strips (R=85 cm): 3.2×1014 neq/cm2 = 8.4 Mrad
Radiation levels after 3000 fb-1
• Radiation hardness requirements (including safety factor of 2)• 2 × 1016 neq/cm2 for the innermost pixel layers
• 7 × 1014 neq/cm2 for the innermost strip layers
Dominated bypion damage
Dominated byneutron damage
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -5-
1013 5 1014 5 1015 5 1016
eq [cm-2]
5000
10000
15000
20000
25000
sign
al [
elec
tron
s]
n-in-n (FZ), 285m, 600V, 23 GeV p p-in-n (FZ), 300m, 500V, 23GeV pp-in-n (FZ), 300m, 500V, neutrons
p-in-n-FZ (500V)n-in-n FZ (600V)
M.Moll - 08/2008
References:
[1] p/n-FZ, 300m, (-30oC, 25ns), strip [Casse 2008][2] n/n-FZ, 285m, (-10oC, 40ns), pixel [Rohe et al. 2005]
FZ Silicon Strip and Pixel Sensors
strip sensorspixel sensors
Signal degradation for LHC Silicon SensorsNote: Measured partly
under different conditions! Lines to guide the eye
(no modeling)!
Strip sensors: max. cumulated fluence for LHC
Pixel sensors: max. cumulated fluence for LHC
Situation in 2005
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -6-
1013 5 1014 5 1015 5 1016
eq [cm-2]
5000
10000
15000
20000
25000
sign
al [
elec
tron
s]
n-in-n (FZ), 285m, 600V, 23 GeV p p-in-n (FZ), 300m, 500V, 23GeV pp-in-n (FZ), 300m, 500V, neutrons
p-in-n-FZ (500V)n-in-n FZ (600V)
M.Moll - 08/2008
References:
[1] p/n-FZ, 300m, (-30oC, 25ns), strip [Casse 2008][2] n/n-FZ, 285m, (-10oC, 40ns), pixel [Rohe et al. 2005]
FZ Silicon Strip and Pixel Sensors
strip sensorspixel sensors
Signal degradation for LHC Silicon SensorsNote: Measured partly
under different conditions! Lines to guide the eye
(no modeling)!
Strip sensors: max. cumulated fluence for LHC and LHC upgrade
Pixel sensors: max. cumulated fluence for LHC and LHC upgrade
LHC upgrade will need more radiation tolerant tracking detector concepts!
Boundary conditions & other challenges:Granularity, Powering, Cooling, Connectivity,
Triggering, Low mass, Low cost!
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -7-
Outline
· Motivation to develop radiation harder detectors · LHC upgrade and expected radiation levels· Radiation induced degradation of detector performance
· Radiation Damage in Silicon Detectors· Microscopic damage (crystal damage), NIEL
· Macroscopic damage (changes in detector properties)
· Approaches to obtain radiation tolerant sensors· Material Engineering
• New silicon materials – FZ, MCZ, DOFZ, EPI• Other semiconductors: Diamond, SiC, GaN, ….
· Device Engineering• p-in-n, n-in-n and n-in-p sensors, 3D sensors and thin devices
· Silicon Sensors for the LHC upgrade ….. open questions and ongoing developments
· Summary
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Radiation Damage – Microscopic Effects
particle
SiS Vacancy + Interstitial
point defects (V-O, C-O, .. )
point defects and clusters of defects
EK>25 eV
EK > 5 keV
V
I
I
I
V
V
¨ Spatial distribution of vacancies created by a 50 keV Si-ion in silicon. (typical recoil energy for 1 MeV neutrons)
van Lint 1980
M.Huhtinen 2001
-8-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Radiation Damage – Microscopic Effects
particle
SiS Vacancy + Interstitial
point defects (V-O, C-O, .. )
point defects and clusters of defects
EK>25 eV
EK > 5 keV
V
I
·Neutrons (elastic scattering)· En > 185 eV for displacement· En > 35 keV for cluster
· 60Co-gammas· Compton Electrons
with max. E 1 MeV (no cluster production)
·Electrons·Ee > 255 keV for displacement·Ee > 8 MeV for cluster
Only point defects point defects & clusters Mainly clusters
10 MeV protons 24 GeV/c protons 1 MeV neutronsSimulation:
Initial distribution of vacancies in (1m)3
after 1014 particles/cm2
[Mika Huhtinen NIMA 491(2002) 194]
-9-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104
particle energy [MeV]
10-5
10-4
10-3
10-2
10-1
100
101
102
103
104
D(E
) / (
95 M
eV m
b)
neutronsneutrons
pionspions
protonsprotons
electronselectrons
100 101 102 103 104
0.4
0.60.8
1
2
4
neutronsneutrons
pionspions
protonsprotons
NIEL - Displacement damage functions
· NIEL - Non Ionizing Energy Loss
· NIEL - Hypothesis: Damage parameters scale with the NIEL· Be careful, does not hold for all particles & damage parameters (see later)
1MeV
11 MeV
neutron equivalent
damage
-11-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -12-
Impact of Defects on Detector Properties
Shockley-Read-Hall statistics
Impact on detector properties can be calculated if all defect parameters are known:n,p : cross sections E : ionization energy Nt : concentration
Trapping (e and h) CCE
shallow defects do not contribute at room
temperature due to fast detrapping
charged defects
Neff , Vdep
e.g. donors in upper and acceptors in lower half of band
gap
generation leakage current
Levels close to midgap
most effective
Details in next lecture by
Ioana Pintilie on defects.
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -13-
Outline
· Motivation to develop radiation harder detectors · LHC upgrade and expected radiation levels· Radiation induced degradation of detector performance
· Radiation Damage in Silicon Detectors· Microscopic damage (crystal damage), NIEL
· Macroscopic damage (changes in detector properties)
· Approaches to obtain radiation tolerant sensors· Material Engineering
• New silicon materials – FZ, MCZ, DOFZ, EPI• Other semiconductors: Diamond, SiC, GaN, ….
· Device Engineering• p-in-n, n-in-n and n-in-p sensors, 3D sensors and thin devices
· Silicon Sensors for the LHC upgrade ….. open questions and ongoing developments
· Summary
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -14-
Impact of Defects on Detector Properties
• Detectors are basically p+- n diodes made on high resistivity silicon
• Standard detector grade silicon:• Float Zone silicon (FZ)• n-type: 220 Kcm • [P] = 2021011 cm-3 (very low concentration !! below 1ppba = 51013cm-3)• [O] several 1015cm-3
• [C] some 1015cm-3 , usually [C] < [O]
• crystal orientation: <111> or <100>
p+
n
n+
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -15-
d ep le ted zo n e
n eu tra l b u lk(n o e lec tric f ie ld )
Poisson’s equation
Reminder: Reverse biased abrupt p+-n junction
Electrical charge density
Electrical field strength
Electron potential energy
effNq
xdx
d
0
02
2
2
0
0 dNq
V effdep
effective space charge density
depletion voltage
Full charge collection only for VB>Vdep !
Positive space charge, Neff =[P](ionized Phosphorus atoms)
p a rtic le (m ip )
+ V < VB d ep + V > VB d ep
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -16-
Macroscopic Effects – I. Depletion Voltage
Change of Depletion Voltage Vdep (Neff)
…. with particle fluence:
• “Type inversion”: Neff changes from positive to
negative (Space Charge Sign Inversion)
10-1 100 101 102 103
eq [ 1012 cm-2 ]
1
510
50100
5001000
5000
Ude
p [V
] (
d =
300
m)
10-1
100
101
102
103
| Nef
f | [
1011
cm
-3 ]
600 V
1014cm-2
type inversion
n-type "p-type"
[M.Moll: Data: R. Wunstorf, PhD thesis 1992, Uni Hamburg]
• Short term: “Beneficial annealing” • Long term: “Reverse annealing” - time constant depends on temperature: ~ 500 years (-10°C) ~ 500 days ( 20°C) ~ 21 hours ( 60°C) - Consequence: Detectors must be cooled even when the experiment is not running!
…. with time (annealing):
NC
NC0
gC eq
NYNA
1 10 100 1000 10000annealing time at 60oC [min]
0
2
4
6
8
10
N
eff [
1011
cm-3
]
[M.Moll, PhD thesis 1999, Uni Hamburg]
after inversion
before inversion n+ p+ n+p+
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -17-
Radiation Damage – II. Leakage Current
1011 1012 1013 1014 1015
eq [cm-2]
10-6
10-5
10-4
10-3
10-2
10-1
I /
V
[A/c
m3 ]
n-type FZ - 7 to 25 Kcmn-type FZ - 7 Kcmn-type FZ - 4 Kcmn-type FZ - 3 Kcm
n-type FZ - 780 cmn-type FZ - 410 cmn-type FZ - 130 cmn-type FZ - 110 cmn-type CZ - 140 cm
p-type EPI - 2 and 4 Kcm
p-type EPI - 380 cm
[M.Moll PhD Thesis][M.Moll PhD Thesis]
· Damage parameter (slope in figure)
Leakage current per unit volume and particle fluence
· is constant over several orders of fluenceand independent of impurity concentration in Si can be used for fluence measurement
eqV
I
α
80 min 60C
Change of Leakage Current (after hadron irradiation)
…. with particle fluence:
· Leakage current decreasing in time (depending on temperature)
· Strong temperature dependence
Consequence: Cool detectors during operation! Example: I(-10°C) ~1/16 I(20°C)
1 10 100 1000 10000annealing time at 60oC [minutes]
0
1
2
3
4
5
6
(t)
[10
-17 A
/cm
]
1
2
3
4
5
6
oxygen enriched silicon [O] = 2.1017 cm-3
parameterisation for standard silicon [M.Moll PhD Thesis]
80 min 60C
…. with time (annealing):
Tk
EI
B
g
2exp
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -18-
Deterioration of Charge Collection Efficiency (CCE) by trapping
tQtQ
heeffhehe
,,0,
1exp)(
0 2.1014 4.1014 6.1014 8.1014 1015
particle fluence - eq [cm-2]
0
0.1
0.2
0.3
0.4
0.5
Inve
rse
trap
ping
tim
e 1
/ [n
s-1]
data for electronsdata for electronsdata for holesdata for holes
24 GeV/c proton irradiation24 GeV/c proton irradiation
[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]
Increase of inverse trapping time (1/) with fluence
Trapping is characterized by an effective trapping time eff for electrons and holes:
….. and change with time (annealing):
5 101 5 102 5 103
annealing time at 60oC [min]
0.1
0.15
0.2
0.25
Inve
rse
trap
ping
tim
e 1
/ [n
s-1]
data for holesdata for holesdata for electronsdata for electrons
24 GeV/c proton irradiation24 GeV/c proton irradiationeq = 4.5.1014 cm-2 eq = 4.5.1014 cm-2
[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]
where defectsheeff
N,
1
Radiation Damage – III. CCE (Trapping)
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -19-
Summary: Radiation Damage in Silicon Sensors
Two general types of radiation damage to the detector materials:
Bulk (Crystal) damage due to Non Ionizing Energy Loss (NIEL) - displacement damage, built up of crystal defects –
I. Change of effective doping concentration (higher depletion voltage, under- depletion)
II. Increase of leakage current (increase of shot noise, thermal runaway)
III. Increase of charge carrier trapping (loss of charge)
Surface damage due to Ionizing Energy Loss (IEL) - accumulation of positive in the oxide (SiO2) and the Si/SiO2 interface – affects: interstrip capacitance (noise factor), breakdown behavior, …
Impact on detector performance and Charge Collection Efficiency (depending on detector type and geometry and readout electronics!)
Signal/noise ratio is the quantity to watch Sensors can fail from radiation damage !
Same for all tested Silicon
materials!
Influenced by impurities
in Si – Defect Engineeringis possible!
Can be optimized!
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
0 10 20 30 40 50 60 70 80Signal [1000 electrons]
0
100
200
300
400
500
600
Cou
nts
[M.Moll][M.Moll]
The charge signal
Collected Charge for a Minimum Ionizing Particle (MIP)
· Mean energy loss dE/dx (Si) = 3.88 MeV/cm 116 keV for 300m thickness
· Most probable energy loss ≈ 0.7 mean 81 keV
· 3.6 eV to create an e-h pair 72 e-h / m (mean) 108 e-h / m (most probable)
· Most probable charge (300 m)
≈ 22500 e ≈ 3.6 fC
Mean charge
Most probable charge ≈ 0.7 mean
noiseCut (threshold)
-20-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Signal to Noise ratio
Good hits selected by requiring NADC > noise tail If cut too high efficiency loss If cut too low noise occupancy
Figure of Merit: Signal-to-Noise Ratio S/N
Typical values >10-15, people get nervous below 10. Radiation damage severely degrades the S/N.
Landau distribution has a low energy tail - becomes even lower by noise broadening
Noise sources: (ENC = Equivalent Noise Charge) - Capacitance - Leakage Current
- Thermal Noise (bias resistor)
dCENC
IENC
RTkENC B
-21-
0 10 20 30 40 50 60 70 80Signal [1000 electrons]
0
200
400
600
800
1000
1200
Cou
nts
non irradiatednon irradiated
p-type MCZ silicon p-type MCZ silicon 5x5 mm2 pad5x5 mm2 pad
90Sr - source90Sr - source
[M.Moll][M.Moll]
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Signal to Noise ratio
Good hits selected by requiring NADC > noise tail If cut too high efficiency loss If cut too low noise occupancy
Figure of Merit: Signal-to-Noise Ratio S/N
Typical values >10-15, people get nervous below 10. Radiation damage severely degrades the S/N.
Landau distribution has a low energy tail - becomes even lower by noise broadening
Noise sources: (ENC = Equivalent Noise Charge) - Capacitance - Leakage Current
- Thermal Noise (bias resistor)
dCENC
IENC
RTkENC B
-22-
0 10 20 30 40 50 60 70 80Signal [1000 electrons]
0
200
400
600
800
1000
1200
Cou
nts
non irradiatednon irradiated
1.1 x 1015 p/cm21.1 x 1015 p/cm2
p-type MCZ silicon p-type MCZ silicon 5x5 mm2 pad5x5 mm2 pad
90Sr - source90Sr - source
[M.Moll][M.Moll]
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
0 10 20 30 40 50 60 70 80Signal [1000 electrons]
0
200
400
600
800
1000
1200
Cou
nts
non irradiatednon irradiated
1.1 x 1015 p/cm21.1 x 1015 p/cm2
9.3 x 1015 p/cm29.3 x 1015 p/cm2
p-type MCZ silicon p-type MCZ silicon 5x5 mm2 pad5x5 mm2 pad
90Sr - source90Sr - source
[M.Moll][M.Moll]
Signal to Noise ratio
Good hits selected by requiring NADC > noise tail If cut too high efficiency loss If cut too low noise occupancy
Figure of Merit: Signal-to-Noise Ratio S/N
Typical values >10-15, people get nervous below 10. Radiation damage severely degrades the S/N.
Landau distribution has a low energy tail - becomes even lower by noise broadening
Noise sources: (ENC = Equivalent Noise Charge) - Capacitance - Leakage Current
- Thermal Noise (bias resistor)
dCENC
IENC
RTkENC B
less signal
mo
re no
ise
What is signal and what is noise?
-23-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -24-
Outline
· Motivation to develop radiation harder detectors · LHC upgrade and expected radiation levels· Radiation induced degradation of detector performance
· Radiation Damage in Silicon Detectors· Microscopic damage (crystal damage), NIEL
· Macroscopic damage (changes in detector properties)
· Approaches to obtain radiation tolerant sensors· Material Engineering
• New silicon materials – FZ, MCZ, DOFZ, EPI• Other semiconductors: Diamond, SiC, GaN, ….
· Device Engineering• p-in-n, n-in-n and n-in-p sensors, 3D sensors and thin devices
· Silicon Sensors for the LHC upgrade ….. open questions and ongoing developments
· Summary
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Approaches to develop radiation harder solid state tracking detectors
· Defect Engineering of Silicon
Deliberate incorporation of impurities or defects into the silicon bulk to improve radiation tolerance of detectors
· Needs: Profound understanding of radiation damage• microscopic defects, macroscopic parameters• dependence on particle type and energy• defect formation kinetics and annealing
· Examples:• Oxygen rich Silicon (DOFZ, Cz, MCZ, EPI)• Oxygen dimer & hydrogen enriched Si• Pre-irradiated Si• Influence of processing technology
· New Materials· Silicon Carbide (SiC), Gallium Nitride (GaN)· Diamond (CERN RD42 Collaboration)· Amorphous silicon
· Device Engineering (New Detector Designs)· p-type silicon detectors (n-in-p)· thin detectors, epitaxial detectors· 3D detectors and Semi 3D detectors, Stripixels· Cost effective detectors· Monolithic devices
Scientific strategies:
I. Material engineering
II. Device engineering
III. Change of detectoroperational conditions
CERN-RD39“Cryogenic Tracking Detectors”operation at 100-200K
to reduce charge loss
-26-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Material: Float Zone Silicon (FZ)
Using a single Si crystal seed, meltthe vertically oriented rod onto the seed using RF power and “pull” themonocrystalline ingot
Wafer production Slicing, lapping, etching, polishing
Mono-crystalline Ingot
Single crystal silicon
Poly silicon rod
RF Heating coil
Float Zone process
Oxygen enrichment (DOFZ) Oxidation of wafer at high temperatures
-28-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Czochralski silicon (Cz) & Epitaxial silicon (EPI)
· Pull Si-crystal from a Si-melt contained in a silica crucible while rotating.
· Silica crucible is dissolving oxygen into the melt high concentration of O in CZ
· Material used by IC industry (cheap) · Recent developments (~5 years) made CZ
available in sufficiently high purity (resistivity) to allow for use as particle detector.
Czochralski Growth
Czochralski silicon
Epitaxial silicon
· Chemical-Vapor Deposition (CVD) of Silicon· CZ silicon substrate used in-diffusion of oxygen· growth rate about 1mm/min· excellent homogeneity of resistivity· up to 150 mm thick layers produced (thicker is possible)· price depending on thickness of epi-layer but not
extending ~ 3 x price of FZ wafer
-29-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
0 10 20 30 40 50 60 70 80 90 100Depth [m]
51016
51017
51018
5
O-c
once
ntra
tion
[1/c
m3 ]
SIMS 25 m SIMS 25 m
25 m
u25
mu
SIMS 50 mSIMS 50 m
50 m
u50
mu
SIMS 75 mSIMS 75 m
75 m
u75
mu
simulation 25 msimulation 25 msimulation 50 msimulation 50 msimulation 75msimulation 75m
Oxygen concentration in FZ, CZ and EPI
DOFZ and CZ silicon Epitaxial silicon
· EPI: Oi and O2i (?) diffusion from substrate into epi-layer during production
· EPI: in-homogeneous oxygen distribution
[G.Lindström et al.,10th European Symposium on Semiconductor Detectors, 12-16 June 2005]
· DOFZ: inhomogeneous oxygen distribution· DOFZ: oxygen content increasing with time
at high temperature
EPIlayer CZ substrate
0 50 100 150 200 250depth [m]
5
1016
5
1017
5
1018
O-c
once
ntra
tion
[cm
-3]
51016
51017
51018
5
DOFZ 72h/1150oCDOFZ 48h/1150oCDOFZ 24h/1150oC
Data: G.Lindstroem et al.
[M.Moll]
· CZ: high Oi (oxygen) and O2i (oxygen dimer) concentration (homogeneous)
· CZ: formation of Thermal Donors possible !
0 50 100 150 200 250depth [m]
5
1016
5
1017
5
1018
O-c
once
ntra
tion
[cm
-3]
51016
51017
51018
5
Cz as grown
DOFZ 72h/1150oCDOFZ 48h/1150oCDOFZ 24h/1150oC
Data: G.Lindstroem et al.
[M.Moll]
-30-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Standard FZ, DOFZ, MCz and Cz silicon
24 GeV/c proton irradiation
· Standard FZ silicon• type inversion at ~ 21013 p/cm2
• strong Neff increase at high fluence
-31-
0 2 4 6 8 10proton fluence [1014 cm-2]
0
200
400
600
800
Vde
p (3
00m
) [V
]0
2
4
6
8
10
12
|Nef
f| [1
012 c
m-3
]
FZ <111>FZ <111>
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Standard FZ, DOFZ, MCz and Cz silicon
24 GeV/c proton irradiation
· Standard FZ silicon• type inversion at ~ 21013 p/cm2
• strong Neff increase at high fluence
· Oxygenated FZ (DOFZ)• type inversion at ~ 21013 p/cm2
• reduced Neff increase at high fluence
-32-
0 2 4 6 8 10proton fluence [1014 cm-2]
0
200
400
600
800
Vde
p (3
00m
) [V
]0
2
4
6
8
10
12
|Nef
f| [1
012 c
m-3
]
FZ <111>FZ <111>DOFZ <111> (72 h 11500C)DOFZ <111> (72 h 11500C)
0 2 4 6 8 10proton fluence [1014 cm-2]
0
200
400
600
800
Vde
p (3
00m
) [V
]0
2
4
6
8
10
12
|Nef
f| [1
012 c
m-3
]
FZ <111>FZ <111>DOFZ <111> (72 h 11500C)DOFZ <111> (72 h 11500C)MCZ <100>MCZ <100> CZ <100> (TD killed) CZ <100> (TD killed)
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010
Standard FZ, DOFZ, MCz and Cz silicon
24 GeV/c proton irradiation
· Standard FZ silicon• type inversion at ~ 21013 p/cm2
• strong Neff increase at high fluence
· Oxygenated FZ (DOFZ)• type inversion at ~ 21013 p/cm2
• reduced Neff increase at high fluence
· CZ silicon and MCZ silicon “no type inversion“ in the overall fluence range
(for experts: there is no “real” type inversion, a more clear understanding of the observed effects is obtained by investigating directly the internal electric field; look for: TCT, MCZ, double junction)
· Common to all materials (after hadron irradiation, not after irradiation): reverse current increase increase of trapping (electrons and holes) within ~ 20%
-33-
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -34-
Proton vs. Neutron irradiation of oxygen rich silicon
· Epitaxial silicon (EPI-DO, 72mm, 170Wcm, diodes)
irradiated with 23 GeV protons or reactor neutrons
0 20 40 60 80 1001 MeV neutron equivalent fluence eq [1014 cm-2]
0
100
200
300
400
500
Vde
p (3
00m
) [V
]
23 GeV protons23 GeV protonsreactor neutronsreactor neutrons
Particle:Particle:
[Data: I.Pintilie et al., NIMA 611 (2009) 52]
[M.Moll][M.Moll]
0 20 40 60 80 1001 MeV neutron equivalent fluence eq [1014 cm-2]
-50
0
50
100
Nef
f [10
12 c
m-3
] 23 GeV protons23 GeV protonsreactor neutronsreactor neutrons
Particle:Particle:
[Data: I.Pintilie et al., NIMA 611 (2009) 52]
[M.Moll][M.Moll]
positive space chargepositive space charge
negative space chargenegative space charge
2
0
0 dNq
V effdep
absolute effective space charge densitydepletion voltage
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -35-
Why is proton and neutron damage different?
particle
SiS Vacancy + Interstitial
point defects (V-O, C-O, .. )
point defects and clusters of defects
EK>25 eV
EK > 5 keV
V
I
10 MeV protons 24 GeV/c protons 1 MeV neutronsSimulation:
Initial distribution of vacancies in (1m)3
after 1014 particles/cm2
[Mika Huhtinen NIMA 491(2002) 194]
· A ‘simplified’ explanation for the ‘compensation effects’· Defect clusters produce predominantly negative space charge· Point defects produce predominantly positive space charge (in ‘oxygen rich’ silicon)
negative
positive
For the experts: Note the NIEL violation
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -36-
Mixed irradiations – Change of Neff
· Exposure of FZ & MCZ silicon sensors to ‘mixed’ irradiations· First step: Irradiation with protons or pions · Second step: Irradiation with neutrons
FZ: Accumulation of damage MCZ: Compensation of damage
[G.Kramberger et al., “Performance of silicon pad detectors after mixed irradiations with neutrons and fast charged hadrons”, NIMA 609 (2009) 142-148]
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -37-
Advantage of non-inverting materialp-in-n detectors (schematic figures!)
Fully depleted detector(non – irradiated):
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -38-
inverted to “p-type”, under-depleted:
• Charge spread – degraded resolution
• Charge loss – reduced CCE
Advantage of non-inverting materialp-in-n detectors (schematic figures!)
Fully depleted detector(non – irradiated):
heavy irradiation
inverted
non-inverted, under-depleted:
• Limited loss in CCE
• Less degradation with under-depletion
non inverted
Be careful, this is a very schematic explanation, reality is more complex !
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -39-
p-on-n silicon, under-depleted:
• Charge spread – degraded resolution
• Charge loss – reduced CCE
p+on-n
Device engineeringp-in-n versus n-in-p (or n-in-n) detectors
n-on-p silicon, under-depleted:
• Limited loss in CCE
• Less degradation with under-depletion
• Collect electrons (3 x faster than holes)
n+on-p
n-type silicon after high fluences:(type inverted)
p-type silicon after high fluences:(still p-type)
Comments:- Instead of n-on-p also n-on-n devices could be used
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -40-
· Dominant junction close to n+ readout strip for FZ n-in-p· For MCZ p-in-n even more complex fields have been reported:
· no “type inversion”(SCSI) = dominant field remains at p implant· “equal double junctions” with almost symmetrical fields on both sides
Reality is more complex: Double junctions
n+on-p
p-type silicon after high fluences:(still “p-type”)
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -41-
FZ n-in-p microstrip detectors (n, p, p - irrad)
· n-in-p microstrip p-type FZ detectors (Micron, 280 or 300mm thick, 80mm pitch, 18mm implant )
· Detectors read-out with 40MHz (SCT 128A)
· CCE: ~7300e (~30%) after ~ 11016cm-2 800V
· n-in-p sensors are strongly considered for ATLAS upgrade (previously p-in-n used)
Sig
nal
(103
ele
ctro
ns)
[A.Affolder, Liverpool, RD50 Workshop, June 2009]
Fluence(1014 n eq/cm2 )
500V
800V
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -42-
FZ n-in-p microstrip detectors (n, p, - p irrad)
· n-in-p microstrip p-type FZ detectors (Micron, 280 or 300mm thick, 80mm pitch, 18mm implant )
· Detectors read-out with 40MHz (SCT 128A)
· CCE: ~7300e (~30%) after ~ 11016cm-2 800V
· n-in-p sensors are strongly considered for ATLAS upgrade (previously p-in-n used)
Sig
nal
(103
ele
ctro
ns)
[A.Affolder, Liverpool, RD50 Workshop, June 2009]
Fluence(1014 n eq/cm2 )0 100 200 300 400 500
time at 80oC[min]
0 500 1000 1500 2000 2500time [days at 20oC]
02468
101214161820
CC
E (
103 e
lect
rons
)
6.8 x 1014cm-2 (proton - 800V)6.8 x 1014cm-2 (proton - 800V)
2.2 x 1015cm-2 (proton - 500 V)2.2 x 1015cm-2 (proton - 500 V)
4.7 x 1015cm-2 (proton - 700 V)4.7 x 1015cm-2 (proton - 700 V)
1.6 x 1015cm-2 (neutron - 600V)1.6 x 1015cm-2 (neutron - 600V)
M.MollM.Moll
[Data: G.Casse et al., NIMA 568 (2006) 46 and RD50 Workshops][Data: G.Casse et al., NIMA 568 (2006) 46 and RD50 Workshops]
· no reverse annealing in CCE measurementsfor neutron and proton irradiated detectors
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -43-
1014 5 1015 5 1016
eq [cm-2]
5
10
15
20
25
Col
lect
ed C
harg
e [1
03 ele
ctro
ns]
n-in-p (FZ), 300m, 500V, 23GeV p [1]n-in-p (FZ), 300m, 500V, neutrons [1,2]n-in-p (FZ), 300m, 500V, 26MeV p [1]n-in-p (FZ), 300m, 800V, 23GeV p [1]n-in-p (FZ), 300m, 800V, neutrons [1,2]n-in-p (FZ), 300m, 800V, 26MeV p [1]
n-in-p-Fz (500V)
n-in-p-Fz (800V)
n-in-p-Fz (1700V)
n-in-p (FZ), 300m, 1700V, neutrons [2]p-in-n (FZ), 300m, 500V, 23GeV p [1]p-in-n (FZ), 300m, 500V, neutrons [1]
p-in-n-FZ (500V)
M.Moll - 09/2009
References:
[1] G.Casse, VERTEX 2008 (p/n-FZ, 300m, (-30oC, 25ns)
[2] I.Mandic et al., NIMA 603 (2009) 263 (p-FZ, 300m, -20oC to -40oC, 25ns)
[3] n/n-FZ, 285m, (-10oC, 40ns), pixel [Rohe et al. 2005][1] 3D, double sided, 250m columns, 300m substrate [Pennicard 2007][2] Diamond [RD42 Collaboration][3] p/n-FZ, 300m, (-30oC, 25ns), strip [Casse 2008]
FZ Silicon Strip Sensors
Good performance of planar sensors at high fluence
· Why do planar silicon sensors with n-strip readout give such high signals after high levels (>1015 cm-2 p/cm2) of irradiation?
· Extrapolation of charge trapping parameters obtained at lower fluences would predict much lower signal!
· Assumption: ‘Charge multiplication effects’ as even CCE > 1 was observed
500V
800V
1700V
· Which voltage can be applied?
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -44-
· “3D” electrodes: - narrow columns along detector thickness,
- diameter: 10mm, distance: 50 - 100mm
· Lateral depletion: - lower depletion voltage needed- thicker detectors possible- fast signal- radiation hard
3D detector - concept
n-columns p-columnswafer surface
n-type substrate
p+
---
++
++
-
-
+
30
0 m
m
n+
p+
50 mm
---
+ +++
--+
3D PLANARp+
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -45-
Passivation
p+ doped
55m pitch
50m
300m
n+ doped
10m
Oxide
n+ doped
Metal
Poly 3m
Oxide
Metal
50m
TEOS oxide 2m
UBM/bump
n-type Si
Passivation
p+ doped
55m pitch
50m
300m
n+ doped
10m
Oxide
n+ doped
Metal
Poly 3m
Oxide
Metal
50m
TEOS oxide 2m
UBM/bump
n-type Si
Example: Testbeam of 3D-DDTC· DDTC – Double sided double type column
[G.F
leta
, RD
50 W
ork
shop
, Ju
ne
2007
]
· Testbeam data – Example: efficiency map[M.Koehler, Freiburg Uni, RD50 Workshop June 09]
· Processing of 3D sensors is challenging,but many good devices with reasonableproduction yield produced.
· Competing e.g. for ATLAS IBL pixel sensors
40V applied~98% efficiency
back column
front column
see lecture by Manuel Lozano
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -46-
Property Diamond GaN 4H SiC Si Eg [eV] 5.5 3.39 3.3 1.12 Ebreakdown [V/cm] 107 4·106 2.2·106 3·105 e [cm2/Vs] 1800 1000 800 1450 h [cm2/Vs] 1200 30 115 450 vsat [cm/s] 2.2·107 - 2·107 0.8·107 e-h energy [eV] 13 8.9 7.6-8.4 3.6 e-h pairs/X0 4.4 ~2-3 4.5 10.1
Use of other semiconductor materials?
· Diamond: wider bandgap
lower leakage current less cooling needed less noise
· Signal produced by m.i.p: Diamond 36 e/mm Si 89 e/mm Si gives more charge than diamond · GaAs, SiC and GaN strong radiation damage observed
no potential material for LHC upgrade detectors (judging on the investigated material)
· Diamond (RD42) good radiation tolerance (see later) already used in LHC beam condition monitoring systems considered as potential detector material for sLHC pixel sensors
poly-CVD Diamond –16 chip ATLAS
pixel module
single crystal CVD Diamond of few cm2
Diamond sensors are heavily used in LHC Experiments for Beam Monitoring
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -47-
Are diamond sensors radiation hard?
[V.Ryjov, CERN ESE Seminar 9.11.2009]
[RD42, LHCC Status Report, Feb. 2010] [RD42, LHCC Status Report, Feb. 2010]
· Most published results on 23 GeV protons
· 70 MeV protons 3 times more damaging than 23 GeV protons
· 25 MeV protons seem to be even more damaging (Preliminary: RD42 about to cross check the data shown to the left)
· In line with NIEL calc. for Diamond [W. de Boer et al. Phys.Status Solidi 204:3009,2007]
23 GeV p70 MeV p
23 GeV p
70 MeV p
26 MeV p
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -56-
Summary – Radiation Damage· Radiation Damage in Silicon Detectors
· Change of Depletion Voltage (internal electric field modifications, “type inversion”, reverse annealing, loss of active volume, …) (can be influenced by defect engineering!)
· Increase of Leakage Current (same for all silicon materials)· Increase of Charge Trapping (same for all silicon materials)
Signal to Noise ratio is quantity to watch (material + geometry + electronics)
· Microscopic defects & Damage scaling factors· Microscopic crystal defects are the origin to detector degradation.· NIEL – Hypothesis used to scale damage of different particles with different energy· Different particles produce different types of defects! (NIEL – violation!)· There has been an enormous progress
in the last 5 years in understanding defects.
· Approaches to obtain radiation tolerant devices:· Material Engineering: - explore and develop new silicon materials
(oxygenated Si)- use of other semiconductors (Diamond)
· Device Engineering: - look for other sensor geometries - 3D, thin sensors, n-in-p, n-in-n, …
Details in next lecture by Ioana Pintilie on defects.
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -57-
Detectors for the LHC upgrade· At fluences up to 1015cm-2 (outer layers – ministrip sensors):
The change of the depletion voltage and the large area to be covered by detectors are major problems.· n-MCZ silicon detectors show good performance in mixed fields due to compensation of
charged hadron damage and neutron damage (Neff compensation) (more work needed)
· p-type silicon microstrip detectors show very encouraging results CCE 6500 e; Feq
= 41015 cm-2, 300mm, immunity against reverse annealing!
This is presently the “most considered option” for the ATLAS SCT upgrade
· At fluences > 1015cm-2 (Innermost tracking layers – pixel sensors)The active thickness of any silicon material is significantly reduced due to trapping. Collection of electrons at electrodes essential: Use n-in-p or n-in-n detectors!· Recent results show that planar silicon sensors might still give sufficient signal,
(still some interest in epitaxial silicon and thin sensor options)· 3D detectors : looks promising, drawback: technology has to be optimized!
Many collaborations and sensor producers working on this.· Diamond has become an interesting option (Higher damage due to low energy protons?)
· Questions to be answered: · a) Can we profit from avalanche effects and control them?· b) Can we profit from compensation effects in mixed fields?· c) Can we understand detector performance on the basis of simulations
using defect parameters as input?
? ? ?
Details in
lecture b
y P
hil A
llport
Michael Moll – MC-PAD Network Training, Ljubljana, 27.9.2010 -58-
Acknowledgements & References· Many thanks to the MC-PAD Network for the invitation to give this lecture
· Most references to particular works given on the slides
· Some additional material taken from the following presentations:· RD50 presentations: http://www.cern.ch/rd50/· Anthony Affolder: Presentations on the RD50 Workshop in June 2009 (sATLAS fluence levels)· Frank Hartmann: Presentation at the VCI conference in February 2010 (Diamond results)
· Books containing chapters about radiation damage in silicon sensors· Helmuth Spieler, “Semiconductor Detector Systems”, Oxford University Press 2005· Frank Hartmann, “Evolution of silicon sensor technology in particle physics”, Springer 2009· L.Rossi, P.Fischer, T.Rohe, N.Wermes “Pixel Detectors”, Springer, 2006· Gerhard Lutz, “Semiconductor radiation detectors”, Springer 1999
· Research collaborations and web sites· The RD50 collaboration (http://www.cern.ch/rd50 ) - Radiation Tolerant Silicon Sensors· The RD39 collaboration – Cryogenic operation of Silicon Sensors· The RD42 collaboration – Diamond detectors· ATLAS IBL, ATLAS and CMS upgrade groups
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